Polyolefins such as high density polyethylene (HDPE) homopolymer and linear low density polyethylene (LLDPE) copolymer can be produced using various combinations of catalyst systems and polymerization processes. In some end-use applications, it can be beneficial for the polymer to have a combination of lower density and low levels of long chain branching. Moreover, it can be beneficial for the catalyst system employed to have a high catalytic activity for olefin polymerization, particularly in the presence of a comonomer. Accordingly, it is to these ends that the present invention is directed.